For a sensor using a piezoelectric film, for example, a structure as disclosed in Japanese Patent Application Laid-Open No. H6-216422 has been known. This sensor has a structure in which a central electrode layer having high rigidity is held between a pair of piezoelectric films and is further sandwiched by outer electrode layers having relatively small rigidity from the outside thereof.
The sensor disclosed in Japanese Patent Application Laid-Open No. H6-216422 deforms in a symmetrically vertical manner when a pressing force is applied to an upper or lower side surface. However, when, for example, the rigidity of the electrode layer on a pressing surface side is small, deformation due to application of the pressing force is absorbed by the electrode layer with the result that the pressing force is not always applied to the piezoelectric film. In addition, when the rigidity of the electrode layer on the side opposite to the pressing surface is large, deformation of the piezoelectric film may sometimes be hindered.
Thus, it is an object of the present invention to provide a piezoelectric film sensor capable of detecting a pressing force with high sensitivity to an object in which a direction of the pressing force is known in advance, and a holding state detecting device provided with the piezoelectric film sensor.